The invention relates to an arrangement comprising a bore-type hobbing cutter and a holding arbor.
As far as the receptacle is concerned in a hobbing machine, a distinction is made between a hole type and a shank type. The cutter body, when of a bore-type design, has a centric hole with a longitudinal groove for positive torque transfer. In this case, a key is disposed in a groove of the holding arbor to interact with the longitudinal groove of the cutter hole. It is also known, however, to cause the cutter hole to intersect a transverse groove at its front-end face to obtain positive torque transfer. In the end, it is also known to obtain positive torque transfer via the front-end face.
The shank-type design has both the cutter body and conical or cylindrical shanks integrally formed at the ends of the cutter body. As a rule, a tool of such a sturdy structure features very high concentricity in running. It is unnecessary to pre-align it on the cutter arbor. A disadvantageous feature, however, is the high expenditure, particularly when the cutter is completely made of cemented carbide. Cutters made from hard material are extremely sensitive to shocks and bumps. When the cutter is damaged it frequently needs to be exchanged.
The most widespread type of hobbing cutters is the bore-type design having a longitudinal groove. These are accommodated by a standard-type holding arbor. The bore has ground centering surfaces, e.g. cylindrical surfaces, in the two end regions, each of which extends over approximately one third of the cutter body length. (It is also known to precisely grind them across the entire wall of the bore, but it requires more machining expenditure). The holding arbor has matching cylindrical, ground seating surfaces. Since the cutter body is slid onto the holding arbor minimal looseness is required between components. This will naturally interfere with concentricity in running. After assembly, there is a need to verify concentricity in running on testing collars of the cutter body which are provided for this purpose. If it does not exist below the tolerance limit prescribed it is common for an operator to align the tool and to effect radial relative displacement between the cutter body and holding arbor for a time until the desired concentricity in running is achieved. In any case, however, the concentricity in running of conventional bore-type hobbing cutters is significantly lower than that of a shank-type design.
It is an object of the invention to create an arrangement of a hobbing cutter and a holding arbor which enables concentricity in running which is as high as that of shank-type hobbing cutters, but avoids the disadvantages of this design.